Starting device fob etecteic motors



Inventor! Rudolph FIBWiedema'nn,

R. F. E. WIEDEMANN STARTING DEVICE FOR ELECTRIC MOTORS Flled Dec a, 1923 His A'Ubornes.

Patented Dec. 8, 1925.

UNITED STATES 1,565,238 PATENT OFFICE.

RUDOLPH F. E. WIEDEMANN, OF NEW YORK, N. Y., ASSIGNO'R T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

STARTING DEVICE FOR ELECTRIC MOTORS.

Application filed December a, 1923. Serial Nb. 679,507.

To all whom it may concern:

Be it known that I, RUDOLPH F. E. VVIEDE- iuANN, a citizen of the United States, resid- 7 mg at New York, in the county of New' York, State of New York, have invented certain new and useful Improvements in Starting Devices for Electric Motors, of which the following is a specification.

This invention relates to improvements in starting devices for electric motors and more particularly to a latching mechanism for enforcing the proper sequence in the operation of a motor starting device which has a starting, a running, and an off position.

One of the principal objects of my inven tion is to provide such a motor starting device with electrically controlled latching mechanism that will prevent connection of the motor directly to the supply lines when the motor starting current exceeds a predetermined value.

More specifically, the object of my invention is provide a motor starting device having a starting, a running, and an off position with latching means for preventing the operation of the starting device to the running position before operation to the starting position and until after the motor start-. ing current has decreased to a predetermined value.

My invention is of particular utility when applied to starting devices for alternating current motors of the compensator type and the advantages of my invention can best be explained by describing its use in connection with a well known type of manually operated starting compensator for induction motors although it will be understood that my invention also may be applied to other types of motor starting devices.

Such a manually operated starting compensator is commonly employed to keep the motor starting current as low as possible during the acceleration period and consists essentially of an auto transformer and a double throw switch'member which has a starting and a running position, and is biased to anofi" position which is intermediate the starting and running positions. Usually the connections are such that when the switch member is in the off positiomthe motor and the auto transformer are entirely disconnected from the power source; when 'it is operated to the starting position, the

motor is connected I0 the powerysource through the auto transformer; and when it is operated to the running position, the motor is connected directly to the source.

In order to enforce the operation of the switch member first to starting position and then to running position, it is customary to provide a latch which cooperates with some moving part of the switch member to prevent initial operation from the ofi position directly to the running position and also for preventing a subsequent slow operation from the starting to the running position which might cause undue arcing at the switch con tacts.

'However, in the operation of compensator starting devices provided with such a latch, particularly when the device is manually operated, there is always the possibility of operating the switch member to the starting position and then at once to the running position before the motor has accelerated to approximately full speed. Such rapid operation to the running position not only may cause a large current inrush which will damage the motor windings and the switch contacts but also may impart a severe mechanical shock to the driven machinery due I to the increased startlng torque of the motor when thus connected directly to the lines. My invention contemplates eliminating the possibility of such an improper operation of the starting device, thereby effectively protecting the motor windings from damage and the driven machinery from undesirable shock.

For a better understanding of my invention, reference is had to the accompanying drawings in which Fig. 1 shows diagrammatically a motor starting device provided with my improved latching mechanism; Fig. 2 is a more detailed view of the electrically controlled latching mechanism; Fig. 3 is a side view of the latching mechanism shown in Fig. 2, and Fig. 4: is a view illustrating the relative positions of the latching mechanism in various phases of operation.

Referring to Fig. 1, the motor starting device comprises a rotatable switch mechanism 10 which carries a. set of starting contacts 11 and a set of running contacts 12. Switch mechanism 10 is biased to the off position in which it is shown in Fig. 1, by the spring 13 and is operable by means of handle 14 to both the starting and the running positions, In the starting position,

contacts 11 engage with the cooperating'sta tionary contact blocks 15 and connectthe high voltage slde of the auto transformer 16 to the power lines 1. and the lowvoltage side of the auto transformer to the motor 18, which as shown, isav three-phase squirrel cage induction motor. In tlre running position, contacts 12 engage with thecoopcrating stationary contact blocks 19 to con nect the motor 18 directly to the power lines 17 The latching mechanism 20 is provided to enforce the proper operation of the switch mechanism 10. As shown more indetail in Figs. 2 and 3, the latching m chanism comprises a member 21 secured to the switch mechanism 10 and moving synchronously therewith and a pair of latches 22 and 23 which cooperate with the member 21to prevent operation of switch mechanism 10 to the running position before operation to the starting position and until after the start ing current of the motor decreases to a predetermined value.

Latch 22 may be ofthe type described in the patent to .Gerkens No. 809,677, and is pivotally supported on the pin 24 and has the lower surface which rides on n ember 21 provided with a series of notches of corrugations. Notch 25 is provided witha square shoulder which prevents initial movement ofthe member 21 to the left and consequently the initial operation of switch mecha nism 10 into the running position bllt,l1() '\V ever, p'ern'iits movement oi. nember21 to the right and operation of switch-mechanism 10 into the starting position shown in full lines in Fig. l. When member 21 is moved to the left from the starting position, it ongages the lnunp 26 on latch 22. Ifthis novement to the left is sutiiciently quick, latch22' will lie/thrown upwards and switch mechanism 10 may be operatedthrough the off position and into the running" position before the latch 22 returns to the initial latching position.

In the running position, the member 21 is held by a square shoulder on the right hand side of notch 27. A relay ,28 having its winding energized responsively to the voltageacross a pair of the'power lines 17, is mechanically connected through a pin and slot mechanism'29 to raise the-latch 22 and release member 21 upon a failure of voltage, thus permitting the switch mechanism 10 to return to the oil position according to its bias.

Latch 23 is rotatably supported on pin 30 and is biased by gravity to the unlatched position in which it rests on stop 31 as shown in Fig. 2. The "lower edge of lat-ch 23'is in the form of a camarrangcd-to ride on finger 32 carried by niember 21. When tll'filllll'ibtil 21is operated to the right into thestarting position, the linger ,n'ioves (he latch "23 into latching position with the hooked end in the path of member 21. The plunger or armature 33 of electromagnet 34 'is pivotally connected to latch 23 by therod which is adjustable in length so that the plunger 32 is raised into the magnetic field of elect'romagnet when the latch 23 is moved into the latching position. Electromagnet 34 may'have its energizing winding permanently connected in series with one of the .primary windings of induction. motor 18 as shown, or maybe energized proportionally to the current in the primary winding in any other desired manner. The winding is thus energized responsively to both the starting and the running current of the motor.

The electromagnet 34- is so designed that when the motor starting current exceeds a predeterminedvalue, the plunger 33 exerts sufficient force to raise'the latch 23 and hold it free from the finger 32, as shown in 4. After the motor has accelerated and the starting current. has decreased to the predetermined value, the plunger 33 is re leased and the bias of latch 23 causes it to drop again intoengagement with the finger 32. As thus constructed and arranged the operation of my improved starting device is as follows:

Assume that ,thepower lines 17 are supplied froma suitable source and that the voltage failure relay 28 has been closed so that the pin and'slot connection 29is'held' in thelposition shown .in Fig. 2. To start the motor, the handle 1 lis 'movm'l to the right to operateswitch.mechanismdflto the starting position .and held there until the motor 18 has accelerated to approximately full speed on the low voltage supplied by the auto transformer 16.

Afterthe motor starting current has decreased below the predetermined value, the electromagnet 34L releases latch 23 and the handle14l may then be moved to the left into the running position with a quick positive movement which clears the latch 22.

The lower cam surface of latch 23 follows the finger 32 during this movement and hence latch is returned to the unlatched this operation is performed slowly, the

latch 22 will intercept the member 21 in the off position and prevent completion of the operation to the running position.

It will thus be seen that I have provided a simple and reliable latching mechanism for the motor starting device which prevents connection of the motor directly to the supply lines until after the motor has been accelerated and the starting current has decreased to a predetermined value.

In accordance with the provisions of the patent statutes, I have described the prin ciple of operation of my invention, together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A starting device for electric motors comprising a switch mechanism freely operable between a starting and an off position and normally operable from the starting through the off to a running position, a member mechanically connected to said switch mechanism to move synchronously therewith, and electrically controlled latching means cooperating with said member for stopping the said switch mechanism in the off position upon operation thereof from the starting position with the motor starting current above a predetermined value.

A, starting device for electric motors comprising a switch mechanism operable between a starting, a running and an off position, the off position being intern'lediate the starting and the running positions, a mem her mechanically connected to said switch mechanism to move synchronously therewith, and latching means cooperating with said member for preventing operation of said switch mechanism from the off position to the running position before operation to the starting position and until after the motor starting current decreases to a predetermined value.

3. A starting device for electric motors comprising a switch mechanism operable between a starting, a running, and an off position, the off position being intermediate the starting and running positions, a latch for preventing a slow operation from the starting position through the off position to the running position, and electrically controlled latching means for stopping the said switch mechanism in the off position upon aquick operation thereof from the starting position when the motor starting current exceeds a predetermined value.

4:. A starting device for electric motors comprising a switch mechanism operable between a starting, a running, and an off psition, a latch biased to unlatched position and arranged to be moved upon operation of said switch mechanism to the starting position to latching position for stopping the said switch mechanism in the off position upon operation of said switch mechanism from the starting to the running positiom and electromagnetic means for maintaining the said latch in latching position while the motor starting current exceeds a predetermined value.

5. A starting device for electric motors comprising a switch mechanism operable between a starting, a running and an off position, a latch for preventing slow operation from the starting to the running position, a second latch biased to unlatched position and having a latching position for stopping the said switch mechanism in the ofl position, means for mechanically operating said second latch to latching position upon op eration of said switch mechanism to starting position, an electromagnet responsive to a predetermined current for holding said latch in latching position, and connections whereby the electromagnet is energized responsively to the motor starting current.

6. A starting device for electric motors comprising a switch mechanism biased to an off position which is between a starting and a running position, latching means coopcrating with av movable part of said switch mechanism for preventing initial operation from the off position to the running position and for preventing subsequent slow operation from the starting to the running position, a second latching means cooperating with the said moving part of the switch for preventing quick operation from the starting to the running position, said second latching means being biased to unlatched position and having a cam surface which is engaged by said moving part to actuate the latch into latching position when the switch is operated to starting position, and an electromagnet for maintaining said second latch in latching position when the motor starting current exceeds a predetermined value.

In witness whereof, I have hereunto set my hand.

RUDOLPH F. E. IVIEDEMANN. 

